The present invention relates to a method and apparatus for detecting the thermal characteristics of a subsurface formation in situ and more particularly to such a method and apparatus adapted to obtain reliable data concerning the thermal conductivity, latent heat and general thermal characteristics of subsurface soil and rock strata in place by the insertion of cryogenic material into the formation without having to follow the conventional practice of taking core samples from which only a very rough approximation of such information can be derived.
A reliable determination of the thermal characteristics of subsurface rock and soil formations is important in many areas of application. Geological studies preparatory to mining, oil well drilling, geothermal prospecting and the like depend significantly on a variety of types of information including the characteristics of thermal conductivity and latent heat in subsurface formations of rock strata and soil. Heretofore, there has been no accurate method and/or apparatus for gathering this information.
Conventional practice calls for the extraction of one or more core samples from the formation under study and the subsequent analysis of such core samples in an effort to determine what the characteristics of the formation are. The information derived form such analysis constitutes merely an educated guess and is unreliable to the extent of being virtually worthless. The major difficulty is that extraction of such core samples usually destroys the crystalline structure of the rock within the sample or causes the soil to lose its integrity thereby precluding observation of the sample in its natural form. Additionally, the extraction of core samples permits the latent heat of the samples to be influenced and therefore changed by passage through other formations during extraction and by subjection to the atmosphere upon removal from the earth.
The applicant's U.S. Pat. No. 3,805,587 entitled "Method And Apparatus For Locating Geothermal Sources Of Energy" discloses a method and apparatus having the capability of determining the location of a subterranean geothermal anomaly. It would be advantageous in the use of the method and apparatus of that patent to have a reliable means for determining the thermal conductivity and latent heat of subsurface formation for use in providing additional information to assist in more accurately determining the depth below the earth's surface of the geothermal anomaly.
Therefore, it has long been recognized that it would be desirable to have a method and apparatus for detecting the thermal characteristics of a subsurface formation in situ without having to extract core samples which do not reflect the natural structure of the rock, latent heat of the formation, and which otherwise fail to provide reliable data useful in conducting geological surveys for a variety of purposes.